Multi-mode indication in subfield in a signal field of a wireless local area network data unit

ABSTRACT

In a method for generating an orthogonal frequency division multiplexing (OFDM) physical layer (PHY) data unit, a signal field of the data unit is generated. The signal field includes a first subfield to indicate a configuration used for transmission of the data unit and a second subfield to indicate information regarding one of a plurality of modes for the data unit. When the configuration is a first configuration, the second subfield indicates information regarding a first mode of the plurality of modes. When the configuration is a second configuration, the second subfield indicates information regarding a second mode of the plurality of modes. The data unit is generated to include a preamble and a data portion. The signal field is included in the preamble. The data portion is generated according to one of i) the information regarding the first mode or ii) the information regarding the second mode.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/957,236, now U.S. Pat. No. 9,246,729, entitled “Multi-Mode Indicationin Subfield in a Signal Field of a Wireless Local Area Network DataUnit,” filed on Aug. 1, 2013, which claims the benefit of U.S.Provisional Patent Application No. 61/679,353, entitled “11ah SIG FieldOverloading Bits” and filed on Aug. 3, 2012, both of which areincorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to multi-mode signal field indications incommunication networks.

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range.

Work has begun on two new standards, IEEE 802.11ah and IEEE 802.11af,each of which will specify wireless network operation in sub-1 GHzfrequencies. Low frequency communication channels are generallycharacterized by better propagation qualities and extended propagationranges compared to transmission at higher frequencies. In the past,sub-1 GHz ranges have not been utilized for wireless communicationnetworks because such frequencies were reserved for other applications(e.g., licensed TV frequency bands, radio frequency band, etc.). Thereare few frequency bands in the sub-1 GHz range that remain unlicensed,with different specific unlicensed frequencies in different geographicalregions. The IEEE 802.11ah Standard will specify wireless operation inavailable unlicensed sub-1GHz frequency bands. The IEEE 802.11afStandard will specify wireless operation in TV White Space (TVWS), i.e.,unused TV channels in sub-1GHz frequency bands.

SUMMARY

In an embodiment, a method for generating an orthogonal frequencydivision multiplexing (OFDM) physical layer (PHY) data unit fortransmission via a communication channel includes generating a signalfield of the data unit to include a first subfield to indicate aconfiguration used for transmission of the data unit and a secondsubfield to indicate information regarding one of a plurality of modesfor the data unit. The method also includes, when the configuration is afirst configuration, generating the second subfield to indicateinformation regarding a first mode of the plurality of modes. The methodfurther includes, when the configuration is a second configuration,generating the second subfield to indicate information regarding asecond mode of the plurality of modes. The method additionally includesgenerating the data unit to include a preamble and a data portion,wherein the signal field is included in the preamble, and wherein thedata portion is generated according to one of i) the informationregarding the first mode or ii) the information regarding the secondmode.

In another embodiment, an apparatus comprises a network interfaceconfigured to generate a signal field of the data unit to include afirst subfield to indicate a configuration used for transmission of thedata unit, and a second subfield to indicate information regarding oneof a plurality of modes for the data unit. The network interface is alsoconfigured to, when the configuration is a first configuration, generatethe second subfield to indicate information regarding a first mode ofthe plurality of modes, and when the configuration is a secondconfiguration, generate the second subfield to indicate informationregarding a second mode of the plurality of modes. The network interfaceis further configured to generate the data unit to include a preambleand a data portion. The network interface is further configured toinclude the signal field in the preamble, and generate the data portionaccording to one of i) the information regarding the first mode or ii)the information regarding the second mode.

In yet another embodiment, a method for receiving an orthogonalfrequency division multiplexing (OFDM) physical layer (PHY) data unitvia a communication channel includes receiving a signal field of thedata unit. The method also includes decoding a first subfield of thesignal field, wherein the first subfield indicates a configuration usedfor transmission of the data unit, and decoding a second subfield of thesignal field, wherein the second subfield indicates one a plurality ofmodes associated with the data unit. The method further includesdetermining, based on a value of the first subfield, whether theconfiguration is a first configuration or a second configuration. Themethod further still includes, in response to determining that theconfiguration is a first configuration, determining that the secondsubfield indicates information regarding a first mode of the pluralityof modes and in response to determining that the configuration is asecond configuration, determining that the second subfield indicatesinformation regarding a second mode of the plurality of modes. Themethod additionally includes decoding a data portion of the data unitaccording to one of i) the information regarding the first mode or ii)the information regarding the second mode.

In still another embodiment an apparatus comprises a network interfaceconfigured to receive a signal field of the data unit. The networkinterface is also configured to decode a first subfield of the signalfield, wherein the first subfield indicates a configuration used fortransmission of the data unit, and decode a second subfield of thesignal field, wherein the second subfield indicates one a plurality ofmodes associated with the data unit. The network interface is furtherconfigured to determine, based on a value of the first subfield, whetherthe configuration is a first configuration or a second configuration.The network interface is further still configured to in response todetermining that the configuration is a first configuration, determinethat the second subfield indicates information regarding a first mode ofthe plurality of modes, and in response to determining that theconfiguration is a second configuration, determine that the secondsubfield indicates information regarding a second mode of the pluralityof modes. The network interface is additionally configured to decode adata portion of the data unit according to one of i) the informationregarding the first mode or ii) the information regarding the secondmode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example WLAN in which one or morecommunication devices are configured to utilize multi-mode indicationtechniques described herein, according to an embodiment.

FIG. 2A is a diagram of an example long range data unit having a shortpreamble format, according to one such embodiment.

FIG. 2B is a diagram of an example long range data unit having a longpreamble format, according to an embodiment.

FIG. 3 is a diagram of an example long range data unit having a lowbandwidth preamble format, according to an embodiment.

FIG. 4 is a diagram of a signal field that includes a multi-modesubfield, according to an embodiment.

FIG. 5 is a table listing various subfields of a signal field includedin a short preamble of a single user data unit, a long preamble of asingle user data unit, and a long preamble of a multi-user data unit,according to various embodiments.

FIG. 6 is a table listing various subfields of a signal field of a lowbandwidth preamble, according to an embodiment.

FIG. 7 is a flow diagram of an example method for generating data units,according to an embodiment.

FIG. 8 is a flow diagram of an example method for receiving data units,according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, wireless network devices such as anaccess point (AP) and client devices of a wireless local area network(WLAN) transmit data streams between the AP and the client devices. TheAP is configured to operate with client stations according to at leastone communication protocol. The communication protocol defines operationin a sub-1 GHz frequency range, and is typically used for applicationsrequiring long range wireless communication with relatively low datarates. The communication protocol (e.g., IEEE 802.11ah or IEEE 802.11af)is referred to herein as a “long range” communication protocol. In someembodiments, physical layer (PHY) data units conforming to the longrange communication protocol (“long range data units”) are the same asor similar to “short range” data units conforming to a higher frequency,shorter range communication protocol (e.g., IEEE 802.11n, and/or IEEE802.11ac), but are generated using a lower clock rate (e.g., bydownclocking an IEEE 802.11n or 802.11ac signal). In one embodiment, forexample, the long range communication protocol defines 2 MHz, 4 MHz, 8MHz and 16 MHz data units that are substantially similar to IEEE 802.11nor 802.11ac 20 MHz, 40 MHz, 80 MHz and 160 MHz data units, respectively,and are generated using the same inverse fast Fourier transform (IFFT)size as the respective IEEE 802.11n or 802.11ac data unit, but aregenerated using a ten times slower clock rate than the respective IEEE802.11n or 802.11ac data unit. Like IEEE 802.11n and IEEE 802.11ac shortrange data units, long range data units are transmitted on multiplesubcarriers/tones, using orthogonal frequency division multiplexing(OFDM), over a wireless channel.

In some embodiments, in addition to defining “normal bandwidth” dataunits, such as the 2 MHz, 4 MHz, 8 MHz and 16 MHz described above, longrange communication protocol defines “low bandwidth mode” data unitsthat are transmitted over a bandwidth smaller than any normal modebandwidth channel (e.g., over a 1 MHz bandwidth) and have a lower datarate. In one embodiment where a normal mode 2 MHz or greater data unitis generated using a 64-point or greater IFFT, for example, a lowbandwidth mode 1 MHz data unit is generated using a 32-point IFFT. Thelower data rate of the low bandwidth mode data unit allows the lowbandwidth mode to further extend communication range, which generallyimproves receiver sensitivity, in an embodiment. In various embodiments,the low bandwidth mode is used only as a control mode (e.g., for signalbeacon or association procedures, transmit beamforming trainingoperations, etc.), only for extended range data communications, or both.

In an embodiment, a data unit (e.g., a normal mode data unit or a lowbandwidth mode data) transmitted by the AP includes a preamblecontaining one or more signal fields that carry information required atthe receiver to properly identify and decode the data unit. For example,the signal field includes a mode indication bit (or bits) used toindicate whether a particular mode is being utilized for transmission ofthe data unit. In some embodiments, certain such modes are utilized onlyin some situations (e.g., only in cases of single stream transmissions)and other such modes are utilized in other situations that do notoverlap with the first situations (e.g., only in cases of multi streamtransmissions). In some such embodiments, a single multi-mode subfieldof the signal field is used for indicating both of such modes, and themulti-mode subfield is interpreted based on a value of another subfieldof the signal field (e.g., a subfield that indicates whether the dataunit is a single stream data unit or a multi-stream data unit). Sharingof a subfield of the signal field by two different mode indicationsresults in efficient utilization of limited number of bits available inthe signal field, in at least some embodiments.

FIG. 1 is a block diagram of an example WLAN 10 in which one or morecommunication devices are configured to utilize multi-mode indicationtechniques described herein, according to an embodiment. The WLAN 10includes an AP 14 having a host processor 15 coupled to a networkinterface 16. The network interface 16 includes a medium access control(MAC) processing unit 18 and a physical layer (PHY) processing unit 20.The PHY processing unit 20 includes a plurality of transceivers 21, andthe transceivers 21 are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments.

The WLAN 10 further includes a plurality of client stations 25. Althoughfour client stations 25 are illustrated in FIG. 1, the WLAN 10 caninclude different numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations25 in various scenarios and embodiments. The client station 25-1includes a host processor 26 coupled to a network interface 27. Thenetwork interface 27 includes a MAC processing unit 28 and a PHYprocessing unit 29. The PHY processing unit 29 includes a plurality oftransceivers 30, and the transceivers 30 are coupled to a plurality ofantennas 34. Although three transceivers 30 and three antennas 34 areillustrated in FIG. 1, the client station 25-1 can include differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 and antennas 34 inother embodiments.

In some embodiments, one, some, or all of the client stations 25-2,25-3, and 25-4 has/have a structure the same as or similar to the clientstation 25-1. In these embodiments, the client stations 25 structuredthe same as or similar to the client station 25-1 have the same or adifferent number of transceivers and antennas. For example, the clientstation 25-2 has only two transceivers and two antennas (not shown),according to an embodiment.

In an embodiment, the PHY processing unit 20 of the AP 14 is configuredto generate data units conforming to the long range communicationprotocol, and the transceiver(s) 21 is/are configured to transmit thegenerated data units via the antenna(s) 24. Similarly, the PHYprocessing unit 20 of the AP 14 is configured to process received dataunits conforming to the long range communication protocol, in anembodiment, with the data units being received by the transceiver(s) 24via the antenna(s) 24. Data units conforming to the long range protocolwill be described with reference to FIGS. 4-8 below, according tovarious different embodiments.

In some embodiments, each long range data unit can have one of multipledifferent preamble formats, such as the preamble formats shown in FIGS.2A and 2B. FIG. 2A is a diagram of an example long range data unit 200having a “short preamble” format, according to one such embodiment. Thelong range data unit 200 includes a short preamble 202 and a dataportion 204. In the example embodiment of FIGS. 2A and 2B, the shortpreamble 202 includes an STF 210 with two OFDM symbols, a first LTF(LTF1) 212 with two OFDM symbols, a SIG field 214 with two OFDM symbols,and a total of N−1 additional LTFs (216-1 through 216-N) each having oneOFDM symbol. In an embodiment, the STF 210 is used for packet detectionand automatic gain control, the LTFs 212 and 216-1 through 216-N areused for channel estimation, and the SIG field 214 indicates certain PHYand/or MAC characteristics of the data unit (e.g., length or duration,MCS, etc.). In an embodiment, the short preamble 202 includes one LTFfor each multiple input multiple output (MIMO) spatial stream (e.g., fortwo spatial streams, such that the short preamble 202 includes LTF1 212and LTF2 216-1, but no additional LTFs). In an embodiment, the longrange data unit 200 has the same format as an IEEE 802.11n data unitwith a “Greenfield” preamble format.

FIG. 2B is a diagram of an example long range data unit 220 having a“long preamble” format, according to an embodiment. The long range dataunit 220 includes a long preamble 222 and a data portion 224. In theexample embodiment of FIGS. 2A and 2B, the long preamble 222 includes afirst, legacy STF (L-STF) 230 with two OFDM symbols, a first, legacy LTF(L-LTF1) 232 with two OFDM symbols, a first, legacy SIG (SIGA) field 234with two OFDM symbols, a second, non-legacy STF 240 with one OFDMsymbol, N-1 additional, non-legacy LTFs (242-1 through 242-N) eachhaving one OFDM symbol, and a second, non-legacy SIG (SIGB) field 244with one OFDM symbol. In an embodiment, the long preamble format of longrange data unit 220 is used when in a multi-user mode, and the LTFs 242of the long preamble 222 include one LTF per user. In some embodiments,a receiver can auto-detect whether a long range data unit has the shortor long preamble format by determining the modulation type of one ormore OFDM symbols within the first SIG field (i.e., SIG field 214 inlong range data unit 200, or SIGA field 234 in long range data unit220). In an embodiment, the long range data unit 220 has the same formatas an IEEE 802.11n data unit with a “mixed mode” preamble format, or thesame format as an IEEE 802.11ac data unit.

FIG. 3 is a diagram of an example long range data unit 300 having a “lowbandwidth preamble” format, according to an embodiment. The long rangedata unit 300 includes a low bandwidth preamble 302 and a data portion304. The low bandwidth preamble 302 is similar to the short preamble 202of FIG. 2, but various fields of the low bandwidth preamble 302 arelonger and include greater numbers of OFDM symbols compared to thecorresponding fields of the short preamble 202, in an embodiment. In theexample embodiment of FIG. 3, the low bandwidth preamble 302 includes anSTF 310 with four OFDM symbols, a first LTF (LTF1) 312 with four OFDMsymbols, a SIG field 314 with, depending on the particular embodiment,five or six OFDM symbols, and a total of N-1 additional LTFs (316-1through 316-N) each having one OFDM symbol. In an embodiment, the STF310 is used for packet detection and automatic gain control, the LTFs312 and 316-1 through 316-N are used for channel estimation, and the SIGfield 314 indicates certain PHY and/or MAC characteristics of the dataunit (e.g., length or duration, MCS, etc.). In an embodiment, the lowbandwidth preamble 202 includes one LTF for each multiple input multipleoutput (MIMO) spatial stream (e.g., for two spatial streams, such thatthe low bandwidth preamble 302 includes LTF1 312 and LTF2 316-1, but noadditional LTFs). In an embodiment, the low bandwidth data unit 300 hasthe same format as an IEEE 802.11n data unit with a “Greenfield”preamble format, with at least some of the fields being longer, in termsof OFDM symbols, compared to the corresponding fields of the IEEE802.11n Greenfield preamble format.

In various embodiments, a SIG field of a preamble of a data unit (e.g.,the SIG field 214, the SIGA field 324, the SIGB field 244, the SIG field314) contains PHY and/or MAC information needed by a receiving device toproperly decode the data unit. For example, a SIG field of a preamble ofa data unit includes one or more bits to indicate to the receivingdevice whether a certain PHY mode (e.g., a short guard interval (SGI)mode, beamforming mode, an STBC mode, Doppler mode, etc.) is beingutilized for the data unit. In some embodiments, certain characteristicsindicated in the SIG field are limited to certain configurations. Forexample, some of such characteristics (e.g., modes) are specified foronly certain configurations (e.g., when the number of spatial orspace-time streams is equal to one) and are invalid in otherconfigurations (e.g., when the number of spatial or space-time streamsis greater than one), in an embodiment. Further, some of such modes donot overlap between the configurations, in some embodiments. For examplea first mode is utilized in only in a first configuration (e.g., whenthe number of spatial or space-time streams is equal to one), while asecond mode is utilized in only a second configuration (e.g., when thenumber of spatial or space-time streams is greater than one). In suchembodiments, a multi-mode subfield in a SIG field of a data unit isutilized to indicate each of these modes, and the specific mode beingindicated by the multi-mode subfield is determined based on theparticular configuration being utilized.

FIG. 4 is a diagram of a signal field 350 that includes a multi-modesubfield, according to an embodiment. In an embodiment, the signal field350 corresponds to the SIG field 214 of the data unit 200 of FIG. 2A. Inanother embodiment, the signal field 350 corresponds to the SIG field234 of the data unit 220 of FIG. 2B. In yet another embodiment, thesignal field 530 corresponds to the signal field 314 of the data unit300 of FIG. 3. In other embodiments, the signal field 350 is included inother suitable data units. Similarly, the data units 200, 220, 300include suitable signal fiends other than the signal field 350, in otherembodiment.

In the embodiment of FIG. 3, the signal field 350 includes aconfiguration subfield 352 and a multi-mode subfield 354. Although thesignal field 350 is illustrated as having only one multi-mode subfield354, the signal field 350 includes multiple (e.g., 2, 3, 4, etc.)multi-mode subfields 354 in other embodiments. According to anembodiment, the multi-mode subfield 354 is an “overloaded” subfield thatis used to indicate different non-overlapping modes being utilized forthe current data unit depending the particular configuration indicated,for example, by the configuration subfield 352. For example, for a firstconfiguration (e.g., single spatial or space-time stream configuration),the multi-mode subfield 354 is used to indicate information regarding afirst mode, such as whether or not the first mode is being utilized forthe current data unit (i.e., the data unit that includes the signalfield). Further, for a second configuration (e.g., multiple spatial orspace-time stream configuration), the multi-mode subfield 354 is used toindicate information regarding a second mode, such as whether or not thesecond mode is being utilized for the current data unit. Accordingly, inan embodiment in which the distinguishing characteristic forinterpreting the multi-mode subfield 354 is the number of spatial orspace-time streams, the configuration subfield 352 indicates the numberof spatial or space-time streams used for transmission of the currentdata unit, and the multi-mode subfield 354 is interpreted based on thenumber of spatial or space-time streams indicated by the subfield 352.In other embodiments, the configuration subfield 352 indicates othersuitable configurations that determine interpretation of the multi-modesubfield 354.

As just an example, in an embodiment, the long range communicationspecifies a Doppler mode, the use of which is limited to single streamconfigurations, and a second space time block coding (STBC2) mode, theuse of which is limited to multi stream configurations. In thisembodiment, the multi-mode subfield 354 is used as a Doppler modeindication when the configuration field 352 indicates that a singlespatial space-time stream is used for transmission of the data unit(N_(STS)=1), and is used as a second STBC (STBC2) mode indication whenthe configuration field 352 indicates a multi-stream transmission(N_(STS)>1). In various embodiments, the Doppler mode is used to combathigh Doppler effect communication channels, such as fast changingoutdoor communication channels, for example by introducing travelingpilots into OFDM tones of the data unit (e.g., changing pilot tonepositions on a per symbol basis), or by introducing one or several“midambles” transmitted in a data portion of the data unit to allow areceiving device to obtain new channel estimations during reception ofthe data portion of the data unit or to adjust the channel estimationsobtained at the beginning of the data unit. The STBC2 mode indicates aspace time block code that is optionally utilized for coding a dataportion of the data unit, according to an embodiment. In an embodiment,the Doppler mode is utilized only for single stream transmissions, andis invalid for multi-stream transmissions. On the other hand, the STBC2mode is utilized only for multi-stream transmissions, and is invalid forsingle stream transmissions, in this embodiment.

In this embodiment, when the value of the configuration subfield 352indicates that the number of spatial or space-time streams is equal toone, then the value of the multi-mode subfield 354 indicates informationregarding the Doppler mode, and when the value of the configurationsubfield 352 indicates that the number of spatial or space-time streamsis greater than one, then the value of the multi-mode subfield 354indicates information regarding the STBC2 mode. For example, in thisembodiment, when the value of the configuration subfield 352 indicatesthat the number of spatial or space-time streams is equal to one, avalue of zero (0) of the multi-mode subfield 354 indicates that theDoppler mode is being utilized, and a value of one (1) of the multi-modesubfield 418 indicates that the Doppler mode is not being utilized, orvice versa. In this case, a data portion of the data unit is generatingaccording to whether or not the Doppler mode is used for the data unit,as indicated by the subfield 354, in an embodiment. On the other hand,when the value of the configuration subfield 352 indicates that thenumber of spatial streams is greater than one, then a value of zero (0)of the multi-mode subfield 354 indicates that STBC2 mode is beingutilized, and a value of one (1) of the multi-mode subfield 354indicates that the STBC2 mode is not being utilized, or vice versa, inthis embodiment. In this case, a data portion of the data unit isgenerating according to whether or not the STBC2 mode is used for thedata unit, as indicated by the subfield 354, in an embodiment. Althoughinterpretation of the multi-mode subfield 354 is determined according tothe number spatial or space-time streams in this embodiment, theinterpretation of the multi-mode subfield 354 is determined according toother subfields of the signal field 350 (e.g., the configurationsubfield 352 indicating a parameter other than the number of spatial orspace-time streams), or by means other than a subfield of the signalfield 350, in other embodiments.

In an embodiment, a receiving device (e.g., a client station 25 or theAP14 of FIG. 1) receiving a data unit that includes the signal field 350interprets the subfield 354 based on the value of the subfield 352. Forexample, in an embodiment, the receiving device decodes the subfield 352to determine a value of the subfield 352 and, accordingly, theparticular configuration (e.g., number of spatial or space-time streams)indicated by the subfield 352. The receiving device also decodes themulti-mode subfield 354, and determines the particular mode beingindicated by the multi-mode subfield 354 based on the value of thesubfield 352. For example, in an embodiment in which the subfield 354indicates a number of spatial or space-time streams used fortransmission of the current data unit, when the subfield 354 indicates asingle stream transmission, the receiving device interprets the subfield354 as indicating information regarding a Doppler mode, such as whetheror not the Doppler mode was used to generate the data unit. In thiscase, the receiving device decodes a data portion of the data unit basedon whether or not the Doppler mode was used to generate the data unit,as indicated by the subfield 354, in an embodiment. On the other hand,when the subfield 354 indicates a multi stream transmission, thereceiving device interprets the subfield 354 as indicating informationregarding STBC2 mode, such as whether or not STBC2 mode was using togenerate the data unit, in an embodiment. In this case, the receivingdevice decodes the data portion of the data unit based on whether or notthe STBC2 mode was used to generate the data unit, as indicated by thesubfield 354, in this embodiment. As discussed above, althoughinterpretation of the multi-mode subfield 354 is determined according tothe number spatial or space-time streams in this embodiment, theinterpretation of the multi-mode subfield 354 is determined according toother subfields of the signal field 350 (e.g., the configurationsubfield 352 indicating a parameter other than the number of spatial orspace-time streams), or by means other than a subfield of the signalfield 350, in other embodiments.

With continued reference to FIG. 3, in some embodiments, the signalfield 350 can be included in a single user data unit (e.g., a data unitwith one or more spatial streams transmitted to a single receivingdevice) or in a multi-user data unit (e.g., a data unit with independentspatial streams transmitted to a multiple receiving devices), dependingon a particular scenario or situation. In some such embodiments, thenon-overlapping modes, such as the Doppler mode and the STBC2 modediscussed above, are defined only for single user data units, and areinvalid for multi-user data units. For example, the long rangecommunication protocol specifies that multi-mode subfields are utilizedin signal fields of single user data units and are not utilized insignal fields of multi user data units, in some embodiments. In somesuch embodiments, the signal field 350 excludes the multi-mode subfield354 when the signal 350 is included in a multi-mode data unit. In otherembodiments, one or all of the non-overlapping modes is/are defined forboth single user data units and multi-user data units. In suchembodiments, the signal field 350 includes the multi-mode subfield 354regardless of the type of data unit, i.e., regardless of whether thesignal field 350 is included in a single user data unit or in amulti-user data unit.

FIG. 5 is a table 400 listing various subfields of a signal field 402included in a short preamble (e.g., the SIG field 214 of the data unit200) of a single user data unit (e.g., a data unit that includes one ormore data streams for a single client station), a long preamble (e.g.,the SIG field 234 of the data unit 220) of a single user data unit, anda long preamble (e.g., the SIG field 234 of the data unit 220) of amulti-user data unit (e.g., a data unit that includes independent datastreams for corresponding different receive devices), according tovarious embodiments. In an embodiment, the signal field 402 correspondsto the signal field 350 of FIG. 3. In other embodiments, the signalfield 350 of FIG. 3 omits one or more of the subfields listed in thetable 400 and/or includes one or more additional subfields not listed inthe table 400. In the example embodiment of FIG. 5, in each of the casesillustrated in the table 400, the signal field 402 includes at leastsome of the following subfields: a single-user/multi-user (SU/MU)indication subfield 404 (e.g., 1 bit for long preamble), aLength/Duration subfield 406 (e.g., 9 bits), a modulation and coding(MCS) subfield 408 (e.g., 4 bits), a bandwidth (BW) subfield 410 (e.g.,2 bits), an aggregation subfield 412 (e.g., 1 bit for single user), aspace time block coding (STBC) subfield 414 (e.g., 1-bit), a codingsubfield 416 (e.g., 2 bits for single user, 5 bits for multi-user), ashort guard interval (SGI) subfield 418 (e.g., 1 bit), a groupidentification (GID) subfield 420 (e.g., 6 bits for multi-user), anumber of spatial or space-time streams (N_(STS)) subfield 422 (e.g., 2bits for single user, 8 bits for multi-user (e.g., 2 bits for each of upto four client stations)), a partial association identification (PAID)subfield 424 (e.g., 9 bits for single user), an acknowledgement (Ack)indication subfield 426 (e.g., 2 bits), a smoothing subfield 428 (e.g.,1 bit for short preamble), a beam-change indication subfield 430 (e.g.,1 bit for long preamble, single user), a multi-mode subfield 432 (e.g.,1 bit for single user, 1 bit or not used for multi-user), reserved bits434 (e.g., 3 bits for short preamble, 2 bits for long preamble), CRCbits 436 (e.g., 4 bits), and tail bits 438 (e.g., 6 bits).

Referring to FIG. 4, in an embodiment, the multi-mode subfield 432corresponds to the multi-mode subfield 354, and the N_(STS) subfield 422corresponds to the configuration subfield 352. In this embodiment, themulti-mode subfield 432 is interpreted based on the value of the N_(STS)subfield 422. In other embodiments, the multi-mode subfield 432 isinterpreted based on a value of another subfield of the signal field402, or on information other than information included in the signalfield 402. Further, in the embodiment of FIG. 5, the multi-mode subfield432 is a one-bit subfield in single user data units, with the value ofthe subfield 520 indicating whether a particular mode is being utilizedfor the current data unit. Similarly, in the embodiment of FIG. 4, inmulti-user data units, the multi-mode subfield 432 is either a one bitsubfield or a zero bit subfield, for cases when the non-overlappingmodes apply to multi-mode data units or are invalid for multi-user dataunits, respectively. Although at most one bit is allocated for themulti-mode subfield 432 according to the table 400, other numbers ofbits (e.g., 2, 3, 4, etc.) are allocated for the multi-mode subfield 432in other embodiments. In such embodiments, the multi-mode 432 is capableof indicating other information related to one or more of thenon-overlapping modes indicated by the multi-mode subfield 432, forexample.

FIG. 6 is a table 500 listing various subfields of a signal field 502 ofa low bandwidth preamble (e.g., the SIG field 314 of the data unit 300),according to an embodiment. In an embodiment, the signal field 502corresponds to the signal field 350 of FIG. 3. In other embodiments, thesignal field 350 of FIG. 3 omits one or more of the subfields listed inthe table 500 and/or includes one or more additional subfields notlisted in the table 500. In the example embodiment of FIG. 6, the SIGfield 502 includes the following subfields: a space time block coding(STBC) indication subfield 504 (e.g., 1 bit), a number of spatial orspace time streams (N_(STS)) indication subfield 506 (e.g., 2 bits), ashort guard interval (SGI) subfield 508 (e.g., 1 bit), a coding typeindication field 510 (e.g., 2 bits), a modulation and coding (MCS)subfield 512 (e.g., 4 bits), an aggregation subfield 514 (e.g., 1 bit),a length indication subfield 516 (e.g., 9 bits), a acknowledgement (Ack)indication subfield 518 (e.g., 2 bits), a multi-mode subfield 520 (e.g.,1 bit), reserved bits 522 (e.g., 3 bits), cyclic redundancy check (CRC)bits 524 (e.g., 5 bits, and tail bits subfield 526 (e.g., 6 bits).

Referring to FIG. 4, in an embodiment, the multi-mode subfield 520corresponds to the multi-mode subfield 354, and the N_(STS) subfield 506corresponds to the configuration subfield 352. In this embodiment, themulti-mode subfield 520 is interpreted based on the value of the N_(STS)subfield 506. In other embodiments, the multi-mode subfield 520 isinterpreted based on a value of another subfield of the signal field502, or based on information other than information included in thesignal field 502. Further, in the embodiment of FIG. 6, the multi-modesubfield 520 is a one-bit subfield, with the value of the subfield 520indicating whether a particular mode is being utilized for the currentdata unit. Although only one bit is allocated for the multi-modesubfield 520 according to the table 500, other numbers of bits (e.g., 2,3, 4, etc.) are allocated for the multi-mode subfield 520 in otherembodiments. In such embodiments, the multi-mode 520 is capable ofindicating other information related to one or more of thenon-overlapping modes indicated by the multi-mode subfield 520, forexample.

FIG. 7 is a flow diagram of an example method 700 for generating dataunits, according to an embodiment. The method 700 is implemented by thenetwork interface 16 (e.g., the PHY processing unit 20) (FIG. 1), in anembodiment. The method 700 is implemented by the network interface 27(e.g., the PHY processing unit 29) (FIG. 1), in another embodiment. Inother embodiments, the method 700 is implemented by other suitablenetwork interfaces.

At block 702, a signal field of the data unit is generated. For example,the signal field 350 of FIG. 4 is generated, in an embodiment. Inanother embodiment, another suitable signal field is generated. In anembodiment, the signal field includes some or all of the subfields 402listed in the table 400 of FIG. 5. In another embodiment, the signalfield includes some or all of the subfields 502 listed in the table 500of FIG. 6. In other embodiments, the signal field includes othersuitable subfields in addition to or instead of the subfields listed inthe table 400 or in the table 500.

The signal field generated at block 702 includes a first subfield toindicate a configuration used for transmission of the data unit and asecond subfield to indicate information regarding one of a plurality ofmodes of the data unit. In various embodiments, the second subfieldincludes one bit or a plurality of bits (e.g., 2, 3, 4, 5, etc. bits).In the example embodiment in which the signal field 350 of FIG. 3 isgenerated, the first subfield corresponds to the subfield 352 and thesecond subfield corresponds to the subfield 354. In an embodiment,various modes in the plurality of modes are non-overlapping modes inthat a first mode is utilized only for some values of the first subfieldand a second mode is utilized only for other values of the firstsubfield. As just some examples, in various embodiments, the pluralityof modes includes a Doppler mode, a STBC2 mode, and/or othernon-overlapping modes.

Generating the signal field at block 702 includes operations of block704 or operation of block 706, in an embodiment. Block 704 generallycorresponds to generation of the second subfield when the configurationindicated by the first subfield is a first configuration, and block 704generally corresponds to generation of the second subfield when theconfiguration indicated by the first subfield is a second configuration.More specifically, when the configuration is a first configuration, thesecond subfield is generated at block 704 to indicate informationregarding a first mode of the plurality of modes. On the other hand,when the configuration is a second configuration, the second subfield isgenerated at block 706 to indicate information regarding a second modeof the plurality of modes.

At block 708, the data unit is generated to include a preamble and adata portion. For example, in an embodiment, the data unit 200 of FIG.2A is generated. In another embodiment, the data unit 220 of FIG. 2B isgenerated. In yet another embodiment, the data unit 300 of FIG. 3 isgenerated. In other embodiments, other suitable data units aregenerated. The preamble includes the signal field generated at block702. The data portion is generated according to one of i) theinformation regarding the first mode or ii) the information regardingthe second mode.

FIG. 8 is a flow diagram of an example method 800 for receiving dataunits, according to an embodiment. The method 800 is implemented by thenetwork interface 16 (e.g., the PHY processing unit 20) (FIG. 1), in anembodiment. The method 800 is implemented by the network interface 27(e.g., the PHY processing unit 29) (FIG. 1), in another embodiment. Inother embodiments, the method 800 is implemented by other suitablenetwork interfaces.

At block 802, a signal field of a data unit is received. For example,the signal field 350 of FIG. 4 is received, in an embodiment. In anotherembodiment, another suitable signal field is received. In an embodiment,the signal field includes some or all of the subfields 402 listed in thetable 400 of FIG. 5. In another embodiment, the signal field includessome or all of the subfields 502 listed in the table 500 of FIG. 6. Inother embodiments, the signal field includes other suitable subfields inaddition to or instead of the subfields listed in the table 400 or inthe table 500.

At block 804, a first subfield of the signal field is decoded. The firstsubfield indicates a configuration used for transmission of the dataunit. In an embodiment, the first subfield corresponds to the subfield352 of the signal field 350 of FIG. 4. In an embodiment, the firstsubfield indicates a number of spatial or space time streams used fortransmission of the data unit. In another embodiment, the first subfieldindicates another configuration (or mode) used for transmission of thedata unit.

At block 806, a second subfield of the signal field is decoded. Thesecond subfield indicates one of a plurality of modes for the data unit.In an embodiment, various modes in the plurality of modes arenon-overlapping modes in that a first mode is utilized only for somevalues of the first subfield and a second mode is utilized only forother values of the first subfield. As just some examples, in variousembodiments, the plurality of modes includes a Doppler mode, a STBC2mode, and/or other non-overlapping modes.

At block 808, it is determined whether the first subfield indicates afirst configuration or a second configuration. If it is determined thatthe first subfield indicates a first configuration, the method continuesat block 810, at which it is determined that the second subfieldindicates information regarding the first mode. Then, at block 812, adata portion of the data unit is decoded according to the informationregarding the first mode. On the other hand, if it is determined atblock 808 that the first subfield indicates a second configuration, themethod continues at block 814, at which it is determined that the secondsubfield indicates information regarding the second mode. Then, at block812, a data portion of the data unit is decoded according to theinformation regarding the second mode.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, one or moreprocessors executing firmware instructions, one or more processorsexecuting software instructions, or any combination thereof. Whenimplemented utilizing one or more processors executing software orfirmware instructions, the software or firmware instructions may bestored in any computer readable memory such as on a magnetic disk, anoptical disk, or other storage medium, in a RAM or ROM or flash memory,processor, hard disk drive, optical disk drive, tape drive, etc.Likewise, the software or firmware instructions may be delivered to auser or a system via any known or desired delivery method including, forexample, on a computer readable disk or other transportable computerstorage mechanism or via communication media. Communication mediatypically embodies computer readable instructions, data structures,program modules or other data in a modulated data signal such as acarrier wave or other transport mechanism. The term “modulated datasignal” means a signal that has one or more of its characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media includes wiredmedia such as a wired network or direct-wired connection, and wirelessmedia such as acoustic, radio frequency, infrared and other wirelessmedia. Thus, the software or firmware instructions may be delivered to auser or a system via a communication channel such as a telephone line, aDSL line, a cable television line, a fiber optics line, a wirelesscommunication channel, the Internet, etc. (which are viewed as being thesame as or interchangeable with providing such software via atransportable storage medium). The software or firmware instructions mayinclude machine readable instructions that, when executed by the one ormore processors, cause the one or more processors to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe claims.

What is claimed is:
 1. A method for generating an orthogonal frequencydivision multiplexing (OFDM) physical layer (PHY) data unit fortransmission via a communication channel, the method comprising:generating a signal field of the data unit to include a first subfieldto indicate a configuration used for transmission of the data unit, anda second subfield to indicate information regarding one of a pluralityof modes for the data unit, including: when the configuration is a firstconfiguration, generating the second subfield to indicate informationregarding a first mode of the plurality of modes, and when theconfiguration is a second configuration, generating the second subfieldto indicate information regarding a second mode of the plurality ofmodes; and generating the data unit to include a preamble and a dataportion, wherein the signal field is included in the preamble, andwherein the data portion is generated according to one of i) theinformation regarding the first mode or ii) the information regardingthe second mode.